Focusing method

ABSTRACT

A method for presenting focused images at a predetermined magnification in an optical system having narrow format and fixed object and image planes. The lens with a nominal focal length suitable for the system is manipulated according to the invention by rotating it to change the total conjugate of the optical system while maintaining a fixed physical distance along the principal ray of the imaging system between the object and image planes.

BEO QQS Waited State Jackson [451 May 1, 1973 FOCUSING METHOD Inventor:Earl V. Jackson, Penfield, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

Bausch and Lomb Optical Company, Ophthalmic Lenses: Their History,Theory, and Application, 1935, p. 84. I

[22] Filed: Dec. 29, 1970 Primary Examiner-Samuel S. Matthews Appl. No.:102,460

Assistant ExaminerKenneth C. Hutchison 52 us. Cl...................355/8 350/202 355/49 Enlow, James Ralabae David C. Petre andBarry J. Kesselman 355/49, 54; 350/43, 202; 353/69, 70 A method forpresenting focused images at a predetermined magnification in an opticalsystem having narrow format and fixed object and image planes. The

[56] References Cited lens with a nominal focal length suitable for thesystem is manipulated according to the invention by UNITED STATESPATENTS 3 563 637 2/l971 F 355/46 X rotating it to change the totalconjugate of the optical v erguson......... 5 Stem while maintain. afixed h al di tame 3,468,230 9/1969 .355 5 X Y mg p y S Bellows alongthe principal ray of the imaging system between the object and imageplanes.

3 Claims, 2 Drawing Figures PATENTEU T3373 3.730520 INVENTOR. EARL V.JACKSON M I ATTOR/VEY FOCUSING METHOD This invention relates to opticalsystems and more particularly to precise focusing techniques.

Optical systems exist with constraints in them that prevent theadjustment of physical distance between an object plane and an imageplane. Such constraints may occur in office copying type machinery orother apparatus that for one reason or another has preset object andimage separations and no internal mechanism such as mirrors or prisms tomake finite changes in the total optical conjugate of the system. Onesomewhat constrained system was recently described in copendingapplication Ser. No. 887,453, filed on Dec. 22, 1969 in the names of S.Hoffman et al. This system utilized a multiple exposure imagingapparatus for forming images by the photoelectrophoretic imagingtechnique invented and described in US. Pat. Nos. 3,383,993; 3,384,565and 3,384,566.

These patents disclose how to produce a visual image at one or both oftwo electrodes between which a photoelectrophoretic particle suspensionis placed. The particles are photosensitive and appear to undergo a netchange in charge polarity or a polarity alteration by interaction withone of the electrodes upon exposure to activating electromagneticradiation. The particles will migrate from one of the electrodes underthe influence of an electric field when struck with energy of awavelength within the spectral response curve of the particles.

Therefore, it is an object of this invention to improve opticalapparatus. Another object of this invention is to improve resolutioncapabilities of optical apparatus having narrow formats. Still anotherobject of this invention is to improve resolution capabilities ofmultiple re-exposure systems. A further object of this invention is toimprove resolution of optical apparatus having a fixed total physicaldistance along the principal ray of the imaging system between theobject and image planes. Yet another object is to improve opticalsystems for multiple re-imaging at fixed points and at fixed distancesfrom each other. A further object is to reduce system costs by enablingmoderate tolerances in optical lens components within a constrainedoptical system. Another object is to improve optical systems for use insingle pass photoelectrophoretic imaging apparatus.

These and other objects and advantages of this invention will becomeapparent to those skilled in the art after reading the followingdescription taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic isometric representation of an embodiment of amachine for forming images utilizing this invention; and

FIG. 2 is a diagrammatic illustration of this invention.

This is a method for correcting small focal length differences from thatwhich is required either within a sin gle imaging system or betweenlenses in a multiple imaging system. For example, in a multiple imagingsystem, by rotating the lens through a predetermined angle, the apparentfocal length of one lens can be made exactly equal to that of a lens inanother of the imaging systems. Even for lenses of nominally equal focallength, the exact focal length is probably different and this inventionprovides a correction factor in an optical system by utilizing only thelenses. This eliminates extremely high lens manufacturing tolerances forhighly constrained optical systems.

There are certain terms of art used in conjunction with thephotoelectrophoretic imaging process shown in the embodiment of FIG. 1which should be defined. The injecting electrode is so named because itis thought to inject the electrical charges into activatingphotosensitive particles during imaging. The term photosensitive for thepurpose of this disclosure refers to the property of a particle, whichonce attracted to an injecting electrode, will alter its polarity andmigrate away from the electrode under the influence of an appliedelectric field when exposed to activating electromagnetic radiation. Theterm suspension may be defined as a system having solid particlesdispersed in a solid, liquid or gas. Nevertheless, the suspension usedin the disclosures herein is of the general type having a solidsuspended in a liquid carrier. The term imaging electrode is used todescribe that electrode which interacts which the injecting electrodethrough the suspension and which once contacted by activatedphotosensitive particles will not inject sufficient charges into them tocause them to migrate from the imaging electrode surface. The imagingelectrode is covered with a dielectric surface composed of a material involume resistivity preferably in the order of 10 or greater ohm-cm. anda conductive core member which is preferably a resilient material suchas electrically conductive rubber used to give flexibility to theimaging electrode.

For photoelectrophoretic imaging to occur it is thought that thesesteps, not necessarily in the sequence presented, take place: (I)migration of the particles toward the injecting electrode due to theinfluence of an electric field, (2) the generation of charge carrierswithin the particles when struck by activating radiation within theirspectral response curve, (3) particle deposition on or near theinjecting electrode surface, (4) phenomena associated with the formingof an electrical junction between the particles and injecting electrode,(5) particle charge exchange withthe injecting electrodes, (6)electrophoretic migration-toward the imaging electrode, (7) particledisposition on the imaging electrode. This leaves an optically positiveimage on the contacted surface of the injecting electrode.

The invention herein is described and illustrated in the specificembodiment, in this case a photoelectrophoretic imaging device, havingspecific components listed for carrying out the functions of theapparatus. Nevertheless, the invention need not be thought of as beingconfined to such a specific showing and should be construed broadlywithin the scope of the claims. Any and all equivalents known to thoseskilled in the art can be substituted for the specific apparatus orsteps disclosed as long as the substituted apparatus or steps achieve asimilar function. It may be that other processes or apparatus will beinvented having similar needs to those fulfilled by the apparatus andmethods described and claimed herein, and it is the intention todescribe an invention for possible use in apparatus and systems otherthan the embodiment shown.

Other terms referred to herein relating to the optical system aregenerally meant to have the following definitions. A slit, whetherobject or image, refers to a narrow format for projection having onedimension substantially larger than the other. Such a slit is shown inFIG. 1 by reference numeral 10. The axis of rotation is the axis throughthe center of a lens which is optically parallel to the long dimensionof the object slit or ob ject format. Such an axis is illustrated by thereference numeral 60 in the figures. I

The object plane is the optical plane which when projected through thelens presents a focused image at its conjugate image plane. It is theplane at which an object to be imaged is positioned for projection. Theimage plane is the plane at which the focused imaging light rays areprojected from the object and whereat a photosensitive material may bepositioned and exposed to such light rays. In the figures one such imageplane is the slit 10. Object and image positions are selected at therespective object and image planes of the imaging system.

The principal ray of the optical imaging system is the ray from thecenter of the slit passing through the centers ofthe iris and pupils ofalens.

The schematic representation of FIG. 1 shows a photoelectrophoreticimaging apparatus having an injecting electrode 1 with a coating 2 oftransparent conductive material such as tin oxide on the outside surfaceof the transparent glass member. Such a combination is commerciallyavailable under the name of NESA glass from Pittsburgh Plate GlassCompany of Pittsburgh, Pa. However, other electrically conductivecoatings over transparent substances are suitable for use herein. At afirst imaging area 10, an imaging elec trode l2 interfaces with theouter surface of the injecting electrode 1. As shown, the imagingelectrode carries imaging suspension 13 from the suspension supplyhousing 14 via a suspension application system having a metering roll 15and an applicator roll 16. The imaging suspension is applied to thesurface of the imaging electrode between the injecting electrode 1 andthe imaging electrode 12 at the first imaging area 10.

The imaging electrode 12 has a high dielectric surface 18 overcoated ona conductive flexible inner core 20. A second imaging electrode 22interfaces with the outer surface of the injecting electrode at a secondimaging area 24. Both of the imaging electrodes are connectedrespectively to the negative terminal of electrical sources 25. Theinjecting electrode 1 is shown schematically connected to ground so thata field exists between the two imaging electrodes on the one hand andthe injecting electrode on the other as is the custom for thephotoelectrophoretic imaging process. Further, the second imagingelectrode 22 has a sprayer 32 operatively associated with it to spraycarrier material onto the surface of the second imaging elec trode 22.This aids in selectively removing particles of the suspension from theouter surface of the injecting electrode under the imaging conditionsprovided by the optical system and electrical source. It has been foundthat the addition of materials similar to the liquid carrier of theimaging suspension aids in the migration of particles of the suspensionaway from the injecting electrode in the second imaging area 24.Interfacing with the outer surface 2 of the injecting electrode 1downstream or further along the path of movement of the injectingelectrode is the transfer roller 26 and transfer support sheet 27. Thetransfer roller is electrically connected to a source 28 for causing anopposite polarity to the two imaging electrodes 20 and 22 with theirelectrical source. It is the function of the transfer electrode toelectrophoretically transfer the imaging suspension from the surface 2of the injecting electrode 1 to a support material which is used as thefinal image support media. A cleaning brush 29 is placed in contact withthe outer surface of the injecting electrode 1 to remove any residualsuspension left on the injecting electrode after transfer has beencompleted. Similarly, cleaning brushes 30 and 31 contact the imagingelectrodes 12 and 22 respectively, to clean their surfaces after theinterface with the injecting electrode.

The integrated dual optical system shown herein presents superposedimagewise electromagnetic radiation at each of the plurality ofimagingareas denoted by the numerals 10 and 24. The image is of contiguousportions of the document 34 placed on the document drum 36 at the objectplane of the plurality oflenses 38 and 39. Radiation energy orillumination is supplied by light sources 4043. The two reference lines45 and 46 shown in FIG. 1 represent the principal ray from the objectplane to the image plane of the optical system. It should be noted thatthe document 34 is positioned on a surface of the object drum 36 whichpasses through the object plane of each of the two lenses 38 and 39. Theouter surface 2 of the injecting electrode 1 moves through the imageplane of the two lenses at the imaging areas 10 and 24 respectively. Theprincipal rays 45 and 46 are not the optical axes of each of the lenses.The optical axes, in fact, are shown by the reference lines 48 and 49.With the dual optical system are equal sets of mirrors including planemirrors 50 and 51 and roof mirrors 52 and 53 shown in the respectiveoptical path of the two lenses 38 and 39. The lenses 38 and 39 aremounted for rotational adjustments about their respective axes ofrotation 60 and 61.

Although only two optical systems are shown, it is possible for three ormore to be coordinated in the same manner as shown here to enablemultiple imaging passes with a single revolution of the injectingelectrode past a plurality of imaging electrodes equal to the number ofcoordinated optical systems. The optical systems function to presentmultiple exposures of the document from various places of the objectdrum to various preselected places of the injecting electrode so thatthe same portions of the document are projected at each of the variousprepositions on the injecting electrode which are the predeterminedimage planes. In this three mirrored multiple imaging system, there isthe ability to take two alike curved surfaces functioning as an objectand an image plane and by moving them in synchronous motion produce animage of the objects. The image is optically suitable for transfer tobecome a right reading final image on a sheet of support material. Theobject drum and the image drum can be one continuous transparentcylinder if the magnification of the system is set for one to one or twoseparate cylinders as shown in FIG. 1. If the cylinders are used and oneto one magnification is desired they are of the same diameter and aremechanically locked to be rotated at the same surface velocity making apractical multiple scanning system.

For magnifications different from 1- to 1, the image cylinder radius isequal to the product of the object cylinder radius and the opticalmagnification. Angular velocity and the angle between the imagingstations are equal on both cylinders. Therefore, in a multiple slit-scansystem, the angular velocity of the object and image cylinders are equalfor all magnifications and the radii of the cylinders are in theproportions of the magnifications. For magnifications other than one toone, the chord length or distance between the object slits and adistance between the image slits are different.

In order to have high quality images there must be precise magnificationmatching of the various optical systems. Another requirement for a goodscanning optical system is that the focused image be projected nearlytangentially to the imaging cylinder at the imaging slits to insure theprecise matching of multiple imaging systems or the focusing of thesingle image. These requirements are particularly hard to achieve in anoptical system constrained to a fixed total physical distance separationalong the principal ray between the object and image planes. It isnecessary to make minor adjustments in the total conjugate within thesystem in order to avoid impractical tolerances on the lenses or thesystem and yet enable a high quality image.

FIG. 2 diagrammatically illustrates how this adjustment is accomplishedin the systems improved by this invention. One set of slits such as theimaging slit 24 and the object slit which is imaged thereat are locatedat points C and D in FIG. 2. The total unfolded distance between the twoslits is CD. The normal, total conjugate, is CD cos x FJ. If the lens 38is turned through an angle Y about the axis of rotation 60, the totalconjugate distance equals EK=CD cos (X-Y). Similarly, if the lens isturned through an angle Z, then the total conjugate equals GH=CD cos(X+Z). It can be seen EK is greater than FJ and OH is less than F]. Inthis manner, the total conjugate of the system is adjustable positivelyor negatively to present a focused image of the object even though thereis a fixed physical distance between object and image planes.

The image is limited to the narrowed format indicated by the point atreference C in FIG. 2. Likewise, the object projected is that indicatedby the point representing the slit at reference D. CE, CF and CG areprojections of the image plane extended for positions 62, 63 and 64respectively of the lens. DH, DJ and DK are the respective object planeprojections. If we consider line FJ as the nominal total conjugate, itis clear how the total conjugate can be lengthened, such as EK, orshortened, such as GH. The line CD is the fixed distance principal rayof the object and image positions at the object and image slits. Notethat the rotation of the lens about the axis 60 to achieve the totalconjugate adjustment is parallel to the long format of the slits at Cand D. The general definition of the total conjugate as shown anddescribed above is the distance parallel to the optical axis, which isperpendicular to the nodal plane of the lens (62, 63 or 64), from anobject plane of the lens to a corresponding image plane of the lens at aparticular magnification.

A specific example of the error correction capability of this inventionmay be helpful for illustrative purposes. With the slits at C and D asshown in FIG. 2

equal to 0.250 inch and the distance CD equal to the 39844 inches, thetotal conjugate at the nominal lens position 63 is CD cos x. Ifx equals1730 then CD cos 1730'A equals 38.0. If the lens is turned through anangle Y, the total conjugate becomes EK which equals CD cos (1730'Y).

If one considers this system for imaging a document of standard sizewidth of 9 inches in a constrained system such as that shown in FIG. 1with the following parameters:

magnification 1:1

lensf/4.5 with a 9.5 inch focal length an angle x equal to 1730 an angleof tilt Y equal to 1.75 (to achieve a l percent total conjugatecorrection), and a slit width 10 equal to 0.250 inch the resultingerrors are maximum. The resulting projection error due to a Y focusshift is proportional to Y and reaches a maximum of 0.0008 inch. Theresulting projection error due to a magnification change at the edge ofthe slit (4.5 inches off axis (reference line 45) is proportional toboth angle Y and the document width and reaches a maximum of 0.0018inches. Therefore, the total projection error would equal a maximum of0.0026 inch which by itself would enable a resolution of about 15 linesper millimeter. If the lens had a l percent uncorrected focal lengtherror for the constrained system, the image would be focused 0.18 inchfrom the image plane resulting in a much larger total projection error.

This system provides a method of matching magnifications within aconstrained optical system by adjusting the apparent focal length ofeach of the lenses. This is particularly useful in a productionsituation where it is desirable to prefix a distance such as CD in FIG.2. Of course, the specific changes, values and ranges must be determinedwith regard to the magnification, total conjugate, slit width, formatlength and separation of the image from the optical axis. The exampleabove cites one set of parameters and the adjustment suggested toachieve the results of this invention.

While this invention has been described with reference to the structuresdisclosed herein and while certain theories have been expressed, it isnot confined to the details set forth and this application is intendedto cover such modifications or changes as may come within the purposesof the improvement and the scope of the following claims. What isclaimed is:

1. A method for setting up constrained narrow format scanning opticalprojection systems for producing focused images for superimposing objectdata on an image member including selecting a first narrow formatconstrained scanning optical projection system for projecting moveableobject data from a first fixed object position to a first fixed imageposition having a fixed physical distance along the principal raybetween them;

placing a first lens of the approximately proper focal length for theselected object and image positions at a predetermined position betweenthe object and image positions for projecting a flowing image at thefirst image position;

selecting a second narrow format constrained scanning optical projectionsystem for projecting moveable object data from a second fixed objectposition to a second fixed image position having a fixed physicaldistance along the principal ray between them;

parallel to the long dimension of the narrow format at its predeterminedposition in order to modify its apparent focal length within its opticalsystem to present a matched, focused image relaplacing a second lens ofthe approximately proper tive to the other opticalsystem ffbcal lengthfor seleted f f f h 2" 2. The system of claim 1 wherein the lens isturned Hons at a Predetefmmed posmon t 6 through a maximum angle of 1.75about an axis second scanning optical system such that it prothrough itscenter and optically parallel to the long ects the same ob ect data onthe same position of dimension of the narrow format. the 1mage member asdoes the first scanning opti 10 ml y 3. The system of claim 1 whereinthe ObJBClI format turning at least one of said lenses through an anglea maxlmum ofg Inches by about an axis through its center and optically

1. A method for setting up constrained narrow format scanning opticalprojection systems for producing focused images for superimposing objectdata on an image member including selecting a first narrow formatconstrained scanning optical projection system for projecting moveableobject data from a first fixed object position to a first fixed imageposition having a fixed physical distance along the principal raybetween them; placing a first lens of the approximately proper focallength for the selected object and image positions at a predeterminedposition between the object and image positions for projecting a flowingimage at the first image position; selecting a second narrow formatconstrained scanning optical projection system for projecting moveableobject data from a second fixed object position to a second fixed imageposition having a fixed physical distance along the principal raybetween them; placing a second lens of the approximately proper focallength for the selected object and image positions at a predeterminedposition within the second scanning optical system such that it projectsthe same object data on the same position of the image member as doesthe first scanning optical system; turning at least one of said lensesthrough an angle about an axis through its center and optically parallelto the long dimension of the narrow format at its predetermined positionin order to modify its apparent focal length within its optical systemto present a matched, focused image relative to the other opticalsystem.
 2. The system of claim 1 wherein the lens is turned through amaximum angle of 1.75* about an axis through its center and opticallyparallel to the long dimension of the narrow format.
 3. The system ofclaim 1 wherein the object format is a maximum of 9 inches by 0.25 inch.